What is the zone of immunity?

Bibi and Barak

In the zone

During the Iranian nuclear crisis, the concept of a “zone of immunity” has been thrown around a lot. Take, for instance, Ronen Bergman’s widely-read January piece in the NYT:

[Ehud Barak] warned that no more than one year remains to stop Iran from obtaining nuclear weaponry. This is because it is close to entering its “immunity zone” — a term coined by Barak that refers to the point when Iran’s accumulated know-how, raw materials, experience and equipment (as well as the distribution of materials among its underground facilities) — will be such that an attack could not derail the nuclear project.

Yet, it’s not clear that the concept is quite coherent.

Derail and destroy

First of all, consider that “derail” has no specific meaning. If it means “terminate”, then Iran is already in the zone of immunity. As General Martin Dempsey explained the other day, an Israeli attack would “clearly delay but probably not destroy Iran’s nuclear programme”. The Bush-era CIA director, Michael Hayden, said much the same thing in January: “they [Israel] can’t do it, it’s beyond their capacity”. So what length of delay would constitute a derailment? Without answering this, the zone of immunity blurs into a nebulous concept with little analytical utility.

The second question is why the US or Israeli ability to “derail the nuclear project” should be declining over time. The answers to this usually pertain to three, frequently conflated, activities:

  1. The hardening of Iran’s underground Fordow enrichment facility
  2. The accumulation of enriched uranium, and particularly that enriched to 20 percent i.e., nine-tenths of the way to weapons-grade
  3. The increase in the number of installed centrifuges (e.g. at Fordow, over 1,000 added since May) and therefore latent enrichment capacity

The first of these – the hardening of Fordow – obviously increases Iran’s ability to withstand attack. It is frequently noted that the zone of immunity comes later for the US than for Israel, because of the former’s greater military capabilities. This reinforces the idea that the primary determinant of a zone of immunity is the physical fortification of Fordow. Yet there are vanishingly few news reports which show Iran is actively increasing Fordow’s defenses. Why, then, should Iran be any closer to the zone of immunity today than it was months ago?

This is where the second and third criteria come in. It is usually reports connected to enriched uranium stockpiles and centrifuge installation that drive concerns over the zone of immunity. But things are less clear in this regard. An increase in nuclear materials and installed centrifuges does shorten Iran’s breakout timeline i.e., the time it would take Iran to produce a bomb were the decision to be taken to do so. But what is the relationship between the breakout timeline and a zone of immunity?

Breakout timeline and the zone of immunity

The first argument goes as follows: if an attack only destroys a certain proportion of Fordow’s contents, then more pre-attack materials and centrifuges might mean more surviving, post-attack quantities with which to break out.

This may very well be a factor in assessing immunity, but it would seem to require an unrealistic degree of foresight and precision. It seems reasonable to postulate that any attack would probably have to be premised on an ability to neutralise almost all of Fordow’s contents, not just a middling proportion. Otherwise, Israel would be at high risk of engendering a bombed, embittered Iran with sufficient (or near-sufficient) short-term capability to produce weapons-grade uranium. And if that’s so, does it make a substantial difference whether Iran has 1,000 or 2,000 centrifuges?

The second argument is this: a shorter breakout timeline might allow Iran to pre-empt (note: not withstand) an attack, either by diverting LEU to a clandestine site for further enrichment or by enriching existing LEU at Fordow to weapons-grade, and then diverting the resultant fissile material.

In each of these cases, Iran could only be said to be “immune” from attack if it could undertake and complete these steps before being caught and attacked. Yet, as David Albright explains in reference to the latter scenario: “if only Fordow is used, breakout times are expected to exceed two months as long as the plant utilizes IR-1 centrifuges and current cascade designs”. According to the latest IAEA report, dated 30 August, Iran is indeed only using IR-1 centrifuges (see p5).

Moreover, Iran has taken steps that likely lengthen its breakout timeline. It is Iran’s stockpile of 20% enriched uranium – material that is nine-tenths of the way to weapons-grade – that would be necessary for the most rapid breakout possible. Yet Iran has converted or is converting 97.9kg of this, over half its entire stockpile of the stuff, for fuel plates for the Tehran Research Reactor (IAEA report, p.13). That makes it much harder (and, after irradiation, harder still) to use for weapons purposes. That leaves Iran with just over 91kg, which is not enough for even one bomb. The overarching point is that a timeline measured in months, rather than weeks, is far in excess of the time that it would plausibly take for detection.

That will change over time, particularly if Iran stops diverting 20% enriched uranium for fuel plates and starts using more of its latent enrichment capacity. But, for now, the time it’d take Iran to actually use its spare enrichment capacity to make weapons-grade uranium is far in excess of the time it would take the IAEA (and intelligence agencies) to detect this, and respond (which is not to say that any armed response would be successful over the longer-term).

And all this is without factoring in the considerable amount of time it would take Iran to convert fissile material into a deliverable nuclear device: “Iran would need an estimated 8-12 months to build a crude nuclear explosive that could be tested underground or delivered by non-missile systems”, and even longer for putting a warhead on a ballistic missile (see this, p2).

Why, then, has the New York Times reported on the new IAEA findings by declaring that “Iran is close to crossing what Israel has long said is its red line: the capability to produce nuclear weapons in a location invulnerable to Israeli attack”? Unless we define “close” with much more precision, this seems to be an unnecessarily alarmist judgment. Unless specified with greater detail, the zone of immunity should be understood as a rhetorical device rather than a clearly defined condition.

Final note:

The Wall Street Journal reports that that Iran’s Mohsen Fakhrizadeh, head of Iran’s alleged clandestine weapons programme until 2003 (outlined in some detail in the IAEA’s November report)  is back at work in the northern suburbs of Tehran. The story doesn’t clarify whether Fakhrizadeh is adding much to the activities of what became, after 2003, a “dormant” programme of less sensitive, dual-use activities. Iran, in its typically helpful fashion, has repeatedly blocked the IAEA from interviewing him.

Fakhrizadeh’s activities could be reasonably categorised under  “accumulated know-how”, as Bergman puts it in that NYT piece referenced above. To the extent that these activities accumulate know-how and  shorten the time it would take to eventually fabricate a bomb from fissile material, this does reduce the breakout time. If the breakout time is eventually shortened below the time it takes to detect and respond to breakout, then clandestine research would be taking Iran into the zone of immunity.

But there’s no evidence suggesting that the breakout time is being shortened to that degree. Moreover, the fact that Fakhrizadeh’s return has been clocked (even if you add the usual caveats about judging intelligence leaked by interested parties) perhaps indicates just how difficult it would be for Iran to break out without being detected, given the scale of intelligence efforts against its programme.

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